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Orogens in the Alpine-Himalayan collision zone (AHCZ) exhibit
characteristic diffused seismicity compared to the stable continental
interiors. Interestingly, they also have a thicker-than-average
silica-rich upper crust and total crustal thickness, while their
lithosphere thickness is similar to that of stable continental interiors
(e.g., Tibet, Zagros). These observations provide a metric for the
lithospheric-scale geological inheritance, the role of which we aim to
understand in continental lithosphere dynamics over seismic and geologic
timescales. To achieve this understanding, we use data-driven modelling
to compute the present-day thermomechanical state of the AHCZ lithosphere.
Our results indicate the existence of a critical crustal thickness,
which is thermodynamically controlled by the internal energy and
chemical composition of the crust and is similar to the global average
of continental crust thickness. Orogenic lithospheres with thicknesses
above this critical value possess higher potential energy and are
weakened by the internal energy from heat-producing elements, whereas
continental interior lithospheres with thicknesses close to the critical
crustal thickness are stronger. Weaker orogenic lithospheres respond via
dissipating this energy in a diffused deformation mode, leading to zones
of deformation in contrast to focused deformation at the
plate-boundaries. The observed crustal differentiation in the AHCZ could
be understood as perturbations to the critical crustal thickness caused
by plate-boundary forces. The dynamic evolution of these perturbations
indicates that the critical crustal thickness is a stable fixed-point
attractor in the evolutionary phase-space. |